Method and apparatus for making mosaic targets for electron beams



March 1949. J. B. JOHNSON METHOD AND APPARATUS FOR MAKING MOSAIC TARGETS FOR ELECTRON BEAMS 2 Sheets-Sheet 1 Filed April 29, 1943 FIG. 2

I NVENTOR J. B. JOHNSON 41 1 A TTORNEV March 1, 1949.

Filed A ril 29, 1943 J. B. JOHNSON TARGETS FOR ELECTRON BEAMS 2 Sheets-Sheet 2 E 20 23 I 22 I i /o J a2 6/ 4a 42 4o 4/ O I /4 l HIGH FREQ- :I 'l lylyl llglll 4a 47 44 46 FAST SLOW 45 2 61 LSflflECEaF/Kflfli szzzxwmz 5mm m- WWW vgfi T1 I P50 M4145 INVENTOR JBJOHNSON AT TORNEV Patented Mar. 1, 1949 METHOD AND APPARATUS FOR MAKING MOSAIC TARGETS FOR ELECTRON BEAMS John. B. Johnson, Maplewood, N. 3;, assignor to Be l Telephone Laboratories,

Incorporated,

New York, N. Y., a corporation of New York Application April 29, 1943, Serial No. 484,966

15 Claims. 1

This invention relates to ionic discharge apparatus and more specifically to methods of and means for generating positive ion beams and for utilizing said beams, for example, inthe formation of targets for electron beams in electron camera tubes.

It is an object of this invention to provide novel means for generating and utilizing positive ion beams.

One well-known type-of electron camera tube is called the iconoscope.-" In' the usual form of this tube, there is provided a mosaic target comprising a metal backing or signal plate, an insulating layer on the signal plate, and a discontinuous layer of photosensitized metallic globules or particles on the insulating layer. Radiations from an object are applied to this target and it is scanned with a beam of electrons to produce a signal current in a resistor which is connected to the signal plate. making targets the insulating layer, which usually is of mica or glass, is coated with a metallic layer of silver and by a heating process the silver is broken up into discontinuous particles which are oxidized and sensitized with caesium to form caesium-oxid'e-silver globules. In screens made by this process, the particles are of irregular shape and distribution, thus leading to non-uniformity of photosensitivity over the surface of the mosaic. This invention in one of its primary aspects relates to mosaic targets in which this non-uniformity is avoided or greatly reduced.

It is, accordingly, another object of this invention to provide novel methods of and means for making-mosaic targets forelectrons, thev particles of the mosaics being of substantially uniform shape, size and distribution.

The above objects are attained in accordance with the invention by providing apparatus for generating a beam of positive ions which is modulated or otherwise controlled so that it is cut off in alternate time periods. This beam is caused to scan every elemental areaof an insulating plate to build up thereon metallic particles. The ions may be of a metal which is photosensitive, such as an alkali or alkaline earth metal, or they may be of a metal which is not appreciably photosensitive. In this latter instance, the metallic spots formed by the method are photosensitized as in the usual iconoscope target technique.

More specifically, in accordance with an exemplary form of the invention, the positive ion beam is generated in a side tube connected to In a well-known method of i the camera tube. This side tube comprises an evacuated container enclosing a first electrode member and one or more additional electrode members. Means are provided for vaporizing a suitable metal within the container, and a positive ion discharge is set up within the container which discharge lsformed into a beam of ions by placing the additional electrode members at appropriate negative potentials with respect to the first electrode member to focus the positive ions into a beam. This beam is directed into the tube containing the target to be formed and there utilized as described above.

In a specific method of operation, the metallic ion beam, which is preferably of one of the alkali or alkaline earth-metals, is caused to scan (by electromagnetic or electrostatic means) every elemental area of a desired portion of the insulating blank on which the discontinuous photosensitive elements are to be formed. The beam is varied in intensity during scanning so as to produce a regular pattern. One way of doing this is to cut off the beam in alternate spot scanning periods and also to cut off the beam during alternate line scanning periods so that a regular pattern of dots or squares interspersed with insulating areas is produced; Preferably, the layers of metal are about ten molecules thick. The size of each dot or square is preferably made smaller than a picture element as determined by the size of the electron beam in the electron camera tube although it can beas large as the picture element or even larger. It will take many seconds or even minutes to scan the complete target in order to obtain spots of metal of required thickness. 7

By an alternative method the target can be formed by repeated scanning, that is, a tiny increment of metal is laid down on; each elemental area and this increment is increased by other increments on succeeding scannings until the complete dot structure is built up.

As the photosensitized target loses its sensi-' tivity when exposed to air, the gun system for the electron beam is preferably mounted in the tube before the ionizing process. The gun system for the positive ion beam is mounted in a side tube which is joined to the main tube. A pellet of the metallic material is placed in the side tube and heated, for example, by a coil surrounding the tube. The positive ions are focussed into a beam byfaccelerating anodes (at a negative potential with respect to the first electrode or cathode and the ion beam is caused to scan the target. After the target is sensitized I in connection with the accompanying drawings forming a part thereof in which:

Fig. 1 is a schematic diagram to illustrate a process, in accordance with this invention, of

making a target for an electron camera tube by means of an ion beam;

Fig. 2 is an enlarged, view of a portion of the target for the ion beam;

Fig. 3 is a modification of the arrangement shown in Fig.1; and

Fig. 4 is a circuit diagram showing the connections of the sources of deflecting waves to the deflecting means of the tube of Fig. 3.

Referring more specifically to the drawings, Fig. 1 shows apparatus for forming a positive ion beam and for utilizing this beam to form a mosaic target for electrons, the target being contained in an electron camera tube attached during the process to the tube wherein the ion beam is generated. The main tube I containing the target I4 is shown connected to the auxiliary tube II by means of a narrow neck I2 which is adapted to be out and the ends sealed after the target in the main tube has been formed. The tube It! comprises an evacuated container l3 enclosing the target I'4 which is to have a mosaic surface coated thereon, an electron gun I5 suitable for generating and focussing a beam of electrons upon the target, and two sets otdefiecting elements comprising the magnetic coils I6, l5 and H, H. The electron gun comprises, for example, a cathode 20, a cathode heater 2 I, a control electrode 22, a first anode 23, a second anode 24, and a conducting coating which is preferably placed at the same potential as the second anode 2 The target I4 is placed in position within the camera tube so that it can be struck by the electron beam generated and focussed by the gun I5 and also opposite an opening 26 in the conducting coating 25 through which radiations from an object are adapted to be applied to the target when the tube is finally completed and operating. During the formation of the target l4, however, the electron gun I5 is not operative nor are radiations applied to the target. Target I4 preferably comprises a metal backing plate 30 and a thin layer of mica or glass 3! thereon held to the metal backing plate 30 by any suitable means, such as by screws or clamps (not shown). The insulating coating 3I is adapted to have applied thereto a discontinuous regular pattern of metal particles. This is accomplished by means of an ion beam generated in the side tube II.

The tube II, which is connected to the tube I3 -by means of the neck I 2 at a point thereof somewhere between the. region of the gun I5 and the deflecting coils I6, I6 and I I, I 1, comprises an evacuated container enclosing therein a first electrode 4!, a second electrode 42, and a third electrode 43. The electrode M is shown as a flat" plate while the electrodes 42 and 43 are shown as cylinders, the cylinder 43 being of larger diameter than the cylinder 42. The electrode member 4| is connected to the electrode 42 through a source 44 and two .make-and-break contact members 45 and 46, the purpose of which will be described below. The positive pole of the source 44 is connected to the electrode member 4| and the negative pole thereof is connected through the members 45 and 46 to the electrode member 42. The electrode member 43 is placed at a negative potential with respect to the member 42 by means of a source 41 while the backing plate 39 of the target I4 in the tube I3 is placed at a negative potential with respect to the electrode member 43 by means of a source 48. Within a side tube 49 is placed a metal pellet 50 of any suitable material, such as one of the alkali or alkaline earth metals if it is desired that the target be photosensitive without additional steps, or, if it is desired to photosensitize the target after the metal particles have been formed on the target, another metal, such as magnesium, may be used. The metal pellet 55 can be vaporized by means of the coil 5I placed around the side tube 49 and energized by any suitable source of high frequency current (not shown) or it can be heated by any other suitable means.

The manner in which the apparatus shown in Fig. 1 operates to produce metal particles 52 on the insulating layer 3I of the target I4 is a follows: The tube II is connected to the tube Ill by means of the glass neck I2. If the ion beam is of a material which is photosensitive, or if not photosensitive, it is desired to photosensitize the target while it is in the camera tube, the target cannot be exposed to the air without losing its photosensitivity. For this reason, the electron gun I5 is mounted in the tube Ill and the conducting coating 25 is applied to a portion of the walls of the enclosure I3 by well-known means before the tube I I isjoined to the tube I0. Moreover, the target structure comprising the signal plate 30 and the insulating layer 3I is placed in position before the juncture of these two tubes. A yoke holding the magnetic coils I6, l6 and Il, IT is placed around the tube ID (in some cases it may be desirable to perform this step also before the tube I0 is connected to the tube I I), and magnetic deflecting current is applied to these coils, which current may be of saw-tooth wave form or stepped wave form as will be described more fully below. No potentials are applied to the members of the electron gun I5 as the electron beam does not enter into the process of making the mosaic target coating. A magnetic coil schematically represented in the drawing by the circle. 53 is placed in position so that the beam of ions when formed in the side tube II is directed toward the target I4. A pellet 50 of any suitable material such as vmagnesium is placed in the side tube and this tube sealed off. All gases are then removed from the tube by means of the side tube 54, heat being applied during this step if desired. After all occluded gases are removed from both of the tubes the side tube 54 is sealed off. The heat applied should not be suflicient to .melt the magnesium pellet 50. High frequency currents are then applied to the coil 5I' anclthe pellet 50 is vaporized. With the electrode elements 4|, 42 and 43 connected as shown in the drawing, the element 42 is at a negative potential with respect to the electrode member 4I inasmuch as the top half (as shown in Fig. 1) of. each of the contact members 45 and 46 is of conducting material while the bottom half of each is of non-conducting material. A stream of metallic positive ions is thus formed between the members M and 42. This stream is focussed into a beam by means of the electrostatic fields between members 42 and 43 which are at appropriate negative potentials rent waves passed through the magnetic coils [-6, l6 and l1, l1. After the tiny particles 52 are formed on the insulating layer 3|, the neck [2 is broken and tube It is scaled up, evacuated, and allowed to cool. The magnesium layer is then wholly or partially oxidized by any suitable method and photosensitized as in the process described above. The defiecting plates. 60, 60 and 6|, 6| are left within the tube H]. The process performed by the apparatus of Fig. 3 in some respects is preferable to that of Fig. 1 inasmuch as it is somewhat difiicult to bend an ion beam by electromagnetic means, due to the large mass of the ion as compared with that of the electron, whereas electrostatic deflection may be obtained with field strengths of the order of those commonly used to deflect an electron beam. Another advantage is simplification, the magnetic bending field 53 or an electrostatic equivalent thereof not being required.

When a metal is used which is to be subsequently oxidized and then photosensitized (such a metal, for example, is magnesium), the mosaic pattern can be applied in a separate tube or receptacle and then exposed to the air before being inserted in the cathode ray transmitter tube. The transmitter tube, in this modified arrangement, has means for admitting. the sensitizing metallic vapor but has no positive ion gun associated with it at any stage of the process. In this arrangement, the target is preferably placed at right angles to the beam.

Alternatively, a tube such as tube H of.Fig. 3 can be connected to the tube 10 by means of a rubber hose or similar connection 62. After the target has been coated with the metallic pattern, air can be admitted, the connection 62 broken and the opening sealed up. This alternative method reduces the handling of the target after the first deposit. The tube I is then degassed, oxidized and sensitized in any known manner.

While the invention in its primary aspects relates to a process of or means for forming a mosaic target for use with. an electron beam, it will be appreciated that the invention in its broader aspects is not limited to producing targets; the coating may be provided for some other purpose for which coatings are used. It will be understood also that various modifications can-be made in the specific embodiments described above without departing from the principles upon which the invention is based.

What is claimed is:

1. The combination with a container, of means for producing a vapor of metallic material therein, spaced electrodes within said container between which said vapor is present, a source of potential having its terminals connected to said electrodes respectively whereby positive ions move to one of said electrodes and electrons move to the other of said electrodes, said electrode toward which said positive ions move having an aperture through which some of them pass,and a target for receiving said positive ions, said target com-- prising an element of insulatin material upon which "said positive ions impinge backed by a conducting element electrically connected to said apertured electrode.'

'2. The combination with a container, of means for producing a vapor of metallic material therein, spaced electrodes within said container between which said vapor is present, a source of potential having its terminals connected to said electrodes respectively whereby positive ions move to one of said electrodes and electrons move to the other electrostatically focussing of said electrodes, said electrode towardwhich said positive ions move having .an aperture through which some of them pass, a target for receiving said positive ions, said target comprising an element of insulating material upon which said positive ions impinge backed by a conducting element electrically connected to said apertured electrode, and means for causing said beam to scan said target, whereby said coating is laid down in a progressive manner.

3. The combination with a container, of means for producin a vapor of metallic material therein, spaced electrodes within said container between which said vapor is present, a source of potential having its terminals connected to said electrodes respectively whereby positive ions move to one of said electrodes and electrons move to the other of said electrodes, said electrode toward which said positive ions move having an aperture through which some of them pass, a target for receiving said positive ions, said target comprising an element of insulating material upon which said positive ions impinge backed by a conducting element electrically connected to said apertured electrode, and means for causing said beam to impinge on discrete elemental areas of said target in succession to cause said coating to be laid down in the form of discrete portions forming a regular pattern.

4. The method of making a mosaic target for an electron beam which comprises vaporizing a metal in an evacuated container, ionizing the vapor formed thereby in an electric field produced between'two electrodes in the container, the positive ions formed by said ionization into a beam which is. highly concentrated and of relatively small crosssectional area, causing said beam to scan an insulating surface to lay down a two-dimensional metallic pattern thereon, and photosensitizing the metallic portions of said pattern.

5. The method of making a mosaic target for v sectional area, causing said beam to scan an insulating surface to lay down a uniform two-dimensional metallic pattern thereon, oxidizing the metallic portions of said pattern, and photosensitizing said oxidized metallic portions.

6. The method of making a mosaic target for an electron beam which comprises vaporizing a metal in an evaporated container, ionizing the vapor formed thereby in an electric field produced between two electrodes in the container, electrostatically focussing the positive ions. formed by said ionization into a beam which is highly concentrated and of relatively small vcross-. sectional area, and causing said, beam to scan an insulating surface at the same time that. the beam is being periodically cut ofi at such a rate with respect to the scanning speed that there is laid down'on said surface a two-dimensional uniform pattern of metallic particles separated by insulating spaces.

7. The method of makin a mosaic'target for an electron beam which, comprises vaporizing a metal in an electric field in a highly evacuated container to produce ions focussing and accelerating the positive ones of said ions to'fo'rm a beam of positive ions which is highly concen trated and of relatively small cross-sectional area, and scanning a target surface with said beam while periodically cutting off the beam at such a rate with respect to the scannin speed that the metal is deposited in a regular two-dimensional pattern of small isolated portions.

8. The method of making a mosaic target for an electron beam which comprises vaporizing a metal in an electric field in a highly evacuated container to produce ions, focussing and accelerating the positive ones of said ions to form a beam of positive ions which is highly concentrated and of relatively small cross-sectional area, scanning a target surface with said beam while periodically cutting oiT the beam at such a rate with respect to the scannin speed that the metal is deposited in a regular two-dimensional pattern of small isolated portions, oxidizing the metallic portions of said pattern, and photosensitizing said oxidized metallic portions.

9. In combination, means for forming a beam of positive ions, a target member of insulating material fOr said beam, means for causin said beam to scan said target member, means for causing said beam to impinge on said target member intermittently during said scanning, a metallic element on the opposite side of said target member, and means for giving said metallic element a potential which causes said beam to be accelerated toward said target.

10. In combination, means for forming a beam of positive ions, a target member, means for causing said beam to scan said target member, and means for cutting off said beam periodically many times within the period of time required for the scanning of one line of said target.

11. In combination, means for forming a beam of positive ions, a target member, means for causing said beam to scan said target member, and means for cutting off said beam periodically many times within the period of time required for the scanning of one line of said target and also periodically for complete line intervals.

12. In a gas tight container, means including two apertured electrode members for formin a beam of positive ions which is highly concentrated and of relatively small cross-sectional area, a target member in the path of said beam,

means for causing said beam to scan said target member, and means for applying to said scanning means saw-tooth deflecting waves.

13. In a gas tight container, means including two apertured electrode members for forming a beam of positive ions which is highly concentrated and of relatively small cross-sectional area, a target member in the path of said beam, means for causing said beam to scan said target member, and means for applying to said scanning means deflecting signals having stepped wave forms.

14. In a gas tight container, means including two apertured electrode members for forming a beam of positive ions which is highly concentrated and of relatively small cross-Sectional area, a target member in the path of said beam, means for causing said beam to scan said target member, said scanning means comprising two sets of deflecting elements which cooperate to cause the scanning of a two-dimensional pattern on said target, and means for applying to each of said sets of deflecting elements deflecting signals having stepped wave forms.

15. In a gas tight container, means including two apertured electrode members for forming a beam of positive ions which is highly concentrated and of relatively small cross-sectional area, a target member in the path of said beam, and means for causing said beam to impinge on said target intermittently during said scanning.

JOHN B. JOHNSON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

